This invention relates to a device for testing samples of superconducting material. Specifically, the invention is directed to a read/write magnetic head suitable for determining the local superconducting properties of a sample of material, particularly thin film materials.
The device and methodology herein are related to the device and methodology of an earlier application entitled "Non Contact Test of Materials For Superconductivity" Ser. No. 380,162, filed on July 14, 1989 of which I am a co-inventor. The earlier application was directed to the detection of superconducting transitions in a sample as a whole. The present invention is directed to determining the superconducting properties of various portions of the surface of the sample. Additional background as to the testing of superconducting materials may also be found in application Ser. No. 416,286 entitled "Improved AC Magnetic Susceptometer and Methodology for Analyzing Magnetic Materials" filed Oct. 2, 1989. The disclosure of applications Ser. Nos. 380,162 and 416,286 are incorporated herein by reference as if fully set forth herein.
The discovery of high temperature superconductivity i n Y-Ba-Cu-O has led to unprecedented research activity to find new higher temperature materials as well as to find applications for the existing new materials. In order to test the global superconducting properties of these materials resistivity measurements as well as magnetic tests for flux exclusion or flux expulsion (Meissner effect) are performed. Magnetic testing has the advantage of not requiring electrical contact, but neither test gives an indication of the local properties of the superconducting sample. Critical properties such as the transition temperature (Tc), critical current (Jc), and lower critical field (Hcl) may vary within a sample as a result of variations in composition and stoichiometry. It is important to detect such variations in applications where thin films are applied to electronic devices.
This application describes a magnetic read/write head that is particularly suitable for studying the surface and near surface of superconductors in both bulk and thin film forms. Using this coaxial head, maps of inhomogeneitites in superconducting properties can be generated.